Semiconductor device and method for controlling

ABSTRACT

A semiconductor device is disclosed. The semiconductor device includes a plurality of memory cells provided in a matrix and having a charge storage layer, a plurality of word lines provided on the charge storage layer, and an application section. When reading data from a selected memory cell selected from the plurality of memory cells, the application section applies a voltage having an opposite polarity to the voltage applied to a selected word line to non-selected word lines arranged on both adjacent sides of the selected word line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/341,879, filed on Dec. 22, 2008, now U.S. Pat. No. 8,004,901 entitled“Semiconductor Device and Method for Controlling,” which is herebyincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a semiconductor device and a method forcontrolling thereof, and more particularly to a semiconductor devicehaving a non-volatile memory cell and a method for controlling thereof.

BACKGROUND

Non-volatile memories that are capable of rewriting data have attainedwide use. In a typical type of non-volatile memory, flash memory, atransistor that configures a memory cell stores data by storing electriccharge in a charge storage layer. Floating gate flash memories, that usea floating gate, and silicon oxide nitride oxide silicon (SONOS) flashmemories, in which electric charges are stored in a trap layer made ofsilicon nitride film, use such charge storage layers. One example of theSONOS flash memories, is a flash memory that has a virtual ground memorycell that switches a source and a drain to symmetrically operate.

FIG. 1A is a top view showing an element structure of a flash memoryaccording to a related art example, FIG. 1B is a cross-sectional viewbetween A-A of FIG. 1A, and FIG. 1C is a cross-sectional view betweenB-B of FIG. 1A. FIG. 1A is shown through an ONO film 18. With referenceto FIG. 1A to FIG. 1C, on a semiconductor substrate 10 that is a P-typesilicon substrate (or a semiconductor substrate having a p-type region),a tunnel oxide film 12 made of a silicon oxide film, a charge storagelayer 14 made of a silicon nitride film that is an insulating film, anda top oxide film 16 made of a silicon oxide film are provided. In theaforementioned process, the ONO film 18 is formed on the semiconductorsubstrate 10. On the ONO film 18, a plurality of word lines 20 made ofpolysilicon films, and that also serve as gates are provided so as toextend. In the semiconductor substrate 10, a plurality of bit lines 22that are N-type diffusion regions, and that also serve as sources anddrains are formed so as to extend across the word lines 20.

With reference to FIG. 1A and FIG. 1B, writing of data to a memory cellis described. For example, by rendering a bit line 22 (BL1) as a sourceand a bit line 22 (BL2) as a drain, a high voltage is applied betweenthe bit lines BL1 and BL2. A positive voltage is applied to a word line20 (WL2). Due to hot electron effects, electrons are injected into thecharge storage layer 14, and the electrons (electric charges) can bestored in a charge storage region C1. Further, by switching the sourceand the drain, electrons (electric charges) can be stored in a chargestorage region C2.

When reading data from a memory cell, the threshold voltage of atransistor configuring the memory cell becomes high due to electriccharges stored in a charge storage region. By measuring such thresholdvoltage by current levels, data written in the memory cell can be read.

Japanese Patent Application Publication No. 9-102199 discloses atechnology that, when reading data from a memory cell array having aplurality of memory cells, applies a negative voltage to all word linesof non-selected memory cells coupled to selected memory cells via a bitline to read data only from the selected memory cells. Japanese PatentApplication Publication No. 11-330277 discloses a technology that, whenreading data of a MONOS flash memory, applies a positive voltage to aword line of a memory cell in which data is not read to reduceread-disturbance.

SUMMARY

It is an object of the present invention to provide a semiconductordevice capable of, when reading data from a memory cell, suppressinggeneration of fringe currents and rendering a reading margin large, anda method for controlling thereof.

The semiconductor device includes a plurality of memory cells that areprovided in a matrix and that have a charge storage layer made of aninsulating film that is provided on a semiconductor substrate and aplurality of word lines that are provided on the charge storage layer. Aplurality of memory cells that are arranged in a single line among theplurality of memory cells arranged in the matrix are coupled to the sameword line. The semiconductor device further includes an applicationsection that when reading data from a selected memory cell selected fromthe plurality of memory cells, applies a voltage to a selected word lineto be coupled to the selected memory cell among the plurality of wordlines. The application section applies a voltage that has a polaritythat is opposite to the voltage applied to the selected word line tonon-selected word lines arranged on both adjacent sides of the selectedword line.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments and, together with thedescription, serve to explain the principles of the embodiments:

FIG. 1A is a top view of an element structure of a flash memoryaccording to a related art example.

FIG. 1B is a cross-sectional view of A-A shown in FIG. 1A.

FIG. 1C is a cross-sectional view of B-B shown in FIG. 1A.

FIG. 2 is a block diagram of a flash memory according to one embodiment.

FIG. 3 is a schematic diagram showing a potential distribution of asemiconductor substrate when reading data from a memory cell of theflash memory according to one embodiment.

FIG. 4 is a flowchart of steps performed as a part of the control of avoltage applied to a word line when reading data from a memory cell of aflash memory according to one embodiment.

FIG. 5 is a schematic diagram showing a potential distribution of asemiconductor substrate when reading data from the memory cell of theflash memory according to one embodiment.

FIG. 6 is a simulation result of calculation of the threshold voltage ofa transistor configuring a selected memory cell when reading data fromthe selected memory cell according to one embodiment.

FIG. 7 is a schematic diagram illustrating the selected memory cell usedfor the simulation calculation in FIG. 6 and an adjacent non-selectedmemory cell.

FIG. 8 is a view showing a distribution of the threshold voltage of thetransistor configuring the selected memory cell associated with thesimulation result in FIG. 6.

The drawings referred to in this description should not be understood asbeing drawn to scale except if specifically noted.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. While descriptionswill be provided in conjunction with these embodiments, it will beunderstood that the descriptions are not intended to limit the scope ofthe embodiments. On the contrary, the disclosure is intended to coveralternatives, modifications and equivalents, of these embodiments.Furthermore, in the following description, numerous specific details areset forth in order to provide a thorough understanding of embodiments.In other instances, well-known methods, procedures, components, andcircuits have not been described in detail as not to unnecessarilyobscure aspects of embodiments.

According to a related art example shown in FIG. 1A to FIG. 1C, theplurality of word lines 20 (for example, WL1 to WL3) are provided on thesame charge storage layer 14. Thus, when writing data, as shown in FIG.1A to FIG. 1C, not only electrons pass through a normal channel region17 directly below the word line 20 (WL2) and electric charges are storedin the charge storage region C1, but also electrons pass through anenlarged channel region 19 (such currents are called fringe currents)and electric charges are stored in a charge storage region D in thevicinity of the word line 20 (WL2). Since the charge storage layer 14 ismade of an insulating film, the electrons (electric charges) stored inthe charge storage region C1 and the charge storage region D staytherein.

The charge density of the enlarged channel region 19 is smaller than thecharge density of the normal channel region 17. Thus, fringe currentsare more likely to flow there as compared to currents flowing throughthe normal channel region 17. Thus, when reading data from the memorycell, the threshold voltage of a transistor becomes high due to electriccharges stored in the charge storage region, whereby fringe currentsflow even in a case where, normally, currents do not flow. Thus, theeffective threshold voltage of the transistor decreases. That is, areading margin when reading data becomes small. Particularly, whenelectric charges are stored in the charge storage region D, fringecurrents are more likely to occur.

FIG. 2 is a block diagram of a flash memory according to the comparativeexample. With reference to FIG. 2, in a memory cell array 24, aplurality of memory cells 26 are arranged in a matrix. Gates of aplurality of transistors configuring a plurality of memory cells 26arranged in a single line among the plurality of memory cells 26 arecoupled to the same word line 20. Sources and drains of the plurality oftransistors configuring the plurality of memory cells 26 arranged in asingle column are respectively coupled to the same bit lines 22. Sincean element structure of the flash memory according to the comparativeexample is the same as that of the related art example and is shown inFIG. 1A to FIG. 1C, descriptions thereof are omitted here.

Based on an instruction of a control circuit 36, a high voltagegeneration circuit 34 supplies a voltage for writing, reading, anderasing data. An application section 28 that is an X decoder selects theword line 20, and applies thereto the voltage supplied from the highvoltage generation circuit 34. A Y decoder 30 makes a Y select circuit32 to select the bit line 22. A reading/writing circuit 38 applies thevoltage supplied from the high voltage generation circuit 34 to the bitline 22 via the Y select circuit 32, and writes data input from aninput/output circuit 40 to the memory cells 26 (selected memory cell S).Further, the reading/writing circuit 38 reads data of the selectedmemory cell S, and outputs to the input/output circuit 40. Theinput/output circuit 40 outputs data input from the reading/writingcircuit 38 to the outside, and outputs data input from the outside tothe reading/writing circuit 38.

Next, Table 1 shows a voltage normally used by the application section28 for applying to the word line 20 and a voltage normally used by thereading/writing circuit 38 for applying to the bit line 22 in a casewhen writing data to the selected memory cell S and in a case whenreading data from the selected memory cell S in FIG. 2. Moreover, theword line 20 coupled to the selected memory cell S is rendered as theselected word line WL2, and the word lines 20 arranged on both adjacentsides of the selected word line WL2 are rendered as the non-selectedword line WL1 and the non-selected word line WL3. The bit lines 22coupled to the selected memory cell S are rendered as the bit line 22(BL1) and the bit line 22 (BL2).

TABLE 1 Writing Reading WL1 0 [V] 0 [V] WL2 +9.0 [V]   +4.6 [V]   WL3 0[V] 0 [V] BL1 0 [V] +1.4 [V]   BL2 +4.0 [V]   0 [V]

With reference to Table 1 and FIG. 2, in a case of writing data to theselected memory cell S, the application section 28 applies a voltage of+9.0[V] to the selected word line WL2, and the non-selected word linesWL1 and WL3 are coupled to the ground (0[V]), or made into an openstate. The reading/writing circuit 38 applies a voltage of +4.0[V] tothe bit line 22 (BL2), and the bit Line 22 (BL1) is coupled to theground (0[V]), or made into an open state.

Next, when reading data from the selected memory cell S, the applicationsection 28 applies a voltage of +4.6[V] to the selected word line WL2,and the non-selected word lines WL1 and WL3 are coupled to the ground(0[V]), or made into an open state. The reading/writing circuit 38applies a voltage of +1.4[V] to the bit line 22 (BL1), and the bit line22 (BL2) is coupled to the ground (0[V]), or made into an open state.

FIG. 3 shows a potential size at each position of the semiconductorsubstrate 10 when reading data from the selected memory cell S. Withreference to FIG. 3, a potential of the semiconductor substrate 10directly below the selected word line WL2 has a potential (+Vg[V])obtained by subtracting a voltage that is lowered through the ONO film18 from the voltage (+4.6[V]) applied to the selected word line WL2.Since the non-selected word lines WL1 and WL3 are coupled to the ground(0[V]), a potential of the semiconductor substrate 10 directly below thenon-selected word lines WL1 and WL3 is virtually 0[V]. A potential ofthe semiconductor substrate 10 of a region 42 between the word lines (aregion between the non-selected word line WL1 and the selected word lineWL2, and a region between the selected word line WL2 and thenon-selected word line WL3) varies from +Vg[V] to 0[V] in a curve ofmoderate gradient.

According to the comparative example, as shown in FIG. 1A to FIG. 1C,the selected word line WL2 and the non-selected word lines WL1 and WL3are provided on the same charge storage layer 14. Thus, the potential ofthe semiconductor substrate 10 of the region 42 between the word linesare affected by the voltage applied to the selected word line WL2 andthe non-selected word lines WL1 and WL3. Thus, as shown in FIG. 3, thesemiconductor substrate 10 in the region 42 between the word lines has apositive potential that varies from +Vg[V] to 0[V] in a curve ofmoderate gradient. Consequently, an effective channel width W1 in athreshold voltage +Vt[V] of the transistor configuring the selectedmemory cell S becomes wider compared to a theoretical channel width W2.Thus, the amount of fringe currents flowing through the enlarged channelregion 19 increases as shown in FIG. 1A and FIG. 1C. By the above, sincefringe currents increase in the comparative example, the effectivethreshold voltage of the transistor decreases, and a data reading marginbecomes small.

In order to solve the problems described above, an embodiment of thepresent invention will be described below. A block diagram of a flashmemory according to a first embodiment of the present invention is thesame as that of the comparative example and is shown in FIG. 2, and thusthe description thereof is omitted. Also, an element structure of theflash memory according to the first embodiment is the same as that ofthe comparative example and is shown in FIG. 1A to FIG. 1C, and thus thedescription thereof is omitted.

FIG. 4 is a flow chart showing the control of voltage applied by theapplication section 28 to the word lines 20 when reading data from theselected memory cell S. Table 2 shows voltage applied by the applicationsection 28 to the word lines 20 and voltage applied by thereading/writing circuit 38 to the bit lines 22 when reading data fromthe selected memory cell S. With reference to Table 2, the applicationsection 28 applies a voltage of +4.6[V] to the selected word line WL2,and applies a voltage of −4.6[V] to the non-selected word lines WL1 andWL3. The reading/writing circuit 38 applies a voltage of +1.4[V] to thebit line 22 (BL1), and the bit line 22 (BL2) is coupled to the ground(0[V]), or made into an open state.

TABLE 2 Reading WL1 −4.6 [V] WL2 +4.6 [V] WL3 −4.6 [V] BL1 +1.4 [V] BL2  0 [V]

With reference to FIG. 4, the application section 28 applies a voltageof −4.6[V] to the non-selected word lines WL1 and WL3 (step S10).Thereafter, a voltage of +4.6[V] is applied to the selected word lineWL2 (step S12). After reading data from the selected memory cell Scompletes, the voltage of +4.6[V] applied to the selected word line WL2is released (step S14). Then, the voltage of −4.6[V] applied to thenon-selected word lines WL1 and WL3 are released (step S16).

FIG. 5 shows a potential size at each section of the semiconductorsubstrate 10 when reading data from the selected memory cell S. Withreference to FIG. 5, a potential of the semiconductor substrate 10directly below the selected word line WL2 has a potential (+Vg[V])obtained by subtracting a voltage that is lowered through the ONO film18 from the voltage (+4.6[V]) applied to the selected word line WL2. Apotential of the semiconductor substrate 10 directly below thenon-selected word lines WL1 and WL3 has a potential (−Vg′[V]) obtainedby subtracting a voltage lowered through the ONO film 18 from thevoltage (−4.6 [V]) applied to the non-selected word lines WL1 and WL3. Apotential of the semiconductor substrate 10 in the region 42 between theword lines varies from +Vg[V] to −Vg′[V] in a curve of steep gradient.

According to the first embodiment, as shown in FIG. 1A to FIG. 1C,corresponding to the comparative example, the selected word line WL2 andthe non-selected word lines WL1 and WL3 are provided on the same chargestorage layer 14. Thus, a potential of the semiconductor substrate 10 inthe region 42 between the word lines is affected by the voltage appliedto the selected word line WL2 and the non-selected word lines WL1 andWL3. Also, as shown in Table 2, the application section 28 applies thevoltage of +4.6[V] to the selected word line WL2 to be coupled to theselected memory cell S, and applies the voltage of −4.6[V] that is avoltage having an opposite sign (positive/negative) to the voltageapplied to the selected word line WL2 to the non-selected word lines WL1and WL3 arranged on both adjacent sides of the selected word line WL2.By the above, as shown in FIG. 5, the potential of the semiconductorsubstrate 10 in the region 42 between the word lines varies from +Vg[V]to −Vg′[V] in a curve of steep gradient. Thus, the effective channelwidth W1 in the threshold voltage +Vt[V] of the transistor configuringthe selected memory cell S can be made narrower compared to thecomparative example. Therefore, fringe currents flowing through theenlarged channel region 19 can be suppressed compared to the comparativeexample.

Next, advantageous effects of the first embodiment will be explainedwith reference to FIG. 6. FIG. 6 is a simulation result of calculationof the threshold voltage of the transistor configuring the selectedmemory cell Sin a case when reading data from the selected memory cellS. Also, with reference to FIG. 7, the selected memory cell S used forthe calculation simulation in FIG. 6 and a non-selected memory cell M(see FIG. 2) arranged next to the selected memory cell S will beexplained.

With reference to FIG. 7, a charge storage region NB corresponding to anormally bit (NB) of the selected memory cell S is in a state whereelectric charges are stored (programmed state), and a charge storageregion CB corresponding to a complimentary bit (CB) is in a state whereelectric charges are not stored (erased state). Hereinafter, the chargestorage region NB is expressed as NB (programmed state), and the chargestorage region CB is expressed as CB (erased state). In a state where apositive voltage (for example, +4.6[V]) is applied to the selected wordline WL2, data can be read from NB (programmed state) by coupling thebit line 22 (BL1) to the source and the bit line 22 (BL2) to the drain.Also, data can be read from CB (erased state) by coupling the bit line22 (BL1) to the drain and the bit line 22 (BL2) to the source. Chargedstates of the two charge storage regions (C3 and C4) of the non-selectedmemory cell M are shown in Table 3. The distance between the selectedword line WL2 coupled to the selected memory cell S and the non-selectedword line WL1 coupled to the non-selected memory cell M is 60 nm.

With reference to Table. 3, a state where the charge storage regions C3and C4 are both in an erased state is expressed as an EE state. A statewhere the charge storage region C3 is in an erased state and the chargestorage region C4 is in a programmed state is expressed as an EP state.A state where the charge storage region C3 is in a programmed state andthe charge storage region C4 is in an erased state is expressed as a PEstate. A state where the charge storage regions C3 and C4 are both in aprogrammed state is expressed as a PP state.

TABLE 3 Charge storage region C3 Charge storage region C4 EE stateErased state Erased state EP state Erased state Programmed state PEstate Programmed state Erased state PP state Programmed state Programmedstate

With reference to FIG. 6, the lateral axis shows the size of a voltageapplied to the non-selected word line WL1. The scale on the left side ofthe vertical axis shows the size of the threshold voltage (hereinafter,the threshold voltage of NB) when reading data from NB (programmedstate) and the threshold voltage (hereinafter, the threshold voltage ofCB) when reading data from CB (erased state), and the scale on the rightside shows the difference between the threshold voltage of NB and thethreshold voltage of CB. The thick solid line of FIG. 6 shows thethreshold voltage of NB in each charged state (states of EE, EP, PE, andPP) of the non-selected memory cell M. The thin solid line shows thethreshold voltage of CB in each charged state (states of EE, EP, PE, andPP) of the non-selected memory cell M. The dashed line shows thedifference between the threshold voltage of NB and the threshold voltageCB in each charged state (states of EE, EP, PE, and PP) of thenon-selected memory cell M.

According to FIG. 6, the smaller the voltage applied to the non-selectedword line WL1 is made (absolute value is made large), the larger thethreshold voltage of NB (thick solid line) and the threshold voltage ofCB (thin solid line) becomes. However, the difference (dashed line)between the threshold voltage of NB and the threshold voltage of CB ismade smaller. On the other hand, the distribution of the thresholdvoltage of NB (thick solid line) and the distribution of the thresholdvoltage of CB (thin solid line) is made smaller.

FIG. 8 is a view precisely showing the distribution of the thresholdvoltage of NB and the distribution of the threshold voltage of CB. Withreference to FIG. 8, the scales on the lateral axis and on the left sideof the vertical axis are the same as those in FIG. 6. The scale on theright side of the vertical axis shows the difference between thethreshold voltage of NB (and the threshold voltage of CB) in the statesof EP, PE, and PP, and the threshold voltage of NB (and the thresholdvoltage of CB) in the EE state. Also, the thick solid line and the thinsolid line of FIG. 8 are the same as those in FIG. 6. The thick dashedline shows a value obtained by subtracting the threshold voltage of NB(EE) from the threshold voltage of NB (EP, PE, PP), and the thin dashedline shows a value obtained by subtracting the threshold voltage of CB(EE) from the threshold voltage of CB (EP, PE, PP).

With reference to FIG. 8, the more the voltage applied to thenon-selected word line WL1 is made small (absolute value is made large),the more the value obtained by subtracting the threshold voltage of NB(EE) from the threshold voltage of NB (EP, PE, PP) and the valueobtained by subtracting the threshold voltage of CB (EE) from thethreshold voltage of CB (EP, PE, PP) become closer to 0. That is, whenreading data from the selected memory cell S, by making the voltageapplied to the non-selected word line WL1 small (making the absolutevalue large), the threshold voltage of the transistor configuring theselected memory cell S is hardly affected by the charged state of thenon-selected memory cell M.

Consequently, when reading data from the memory cell array 24 as shownin FIG. 2, even in a case where the memory cells 26 in the programmedstate and in the erased state are randomly existing in the plurality ofmemory cells 26 arranged in a matrix, the distribution of the thresholdvoltage of the transistor configuring the memory cell 26 can be madesmall for the memory cell array 24 as a whole. That is, the distributionof a reading margin can also be made small. Consequently, anadvantageous effect can be obtained in that the reading margin can bemade large when reading data from the memory cell array 24 including theplurality of memory cells 26.

In the first embodiment, as a method for controlling a voltage appliedto the word line 20 by the application section 28 when reading data fromthe selected memory cell S, as shown in FIG. 4, the application section28 applies a voltage having an opposite sign to the voltage applied tothe selected word line WL2 to the non-selected word lines WL1 and WL3(step S10). Thereafter, a voltage is applied to the selected word lineWL2 (step S12). After reading data from the selected memory cell Scompletes, the voltage applied to the selected word line WL2 is released(step S14). Thereafter, a case (step S16) of releasing the voltageapplied to the non-selected word lines WL1 and WL3 is shown. However,the invention is not limited thereto. The method can be of any form aslong as the application section 28 keeps applying a voltage having anopposite sign to the voltage applied to the selected word line WL2 tothe non-selected word lines WL1 and WL3 at least during applying avoltage to the selected word line WL2. For example, a case where theapplication section 28 applies a voltage to the selected word line WL2and the non-selected word lines WL1 and WL3 at the same time. It is alsopossible in this case, as shown in FIG. 5, to narrow the effectivechannel width W1 and suppress fringe currents.

As shown in FIG. 1A and FIG. 1C, a case where the charge storage layer14 is made of a silicon nitride film is shown, however, the invention isnot limited thereto, and the charge storage layer 14 can be made ofother insulating films. Also, a case of storing electrons in the chargestorage layer 14 by hot electron effects is shown. However, theinvention is not limited thereto. In a case where the charge storagelayer 14 is made of an insulating film, and electrons are stored in thecharges storage layer 14 by hot electron effects, as shown in FIG. 1Aand FIG. 1C, electrons (electric charges) are stored in the chargestorage region C1 and the charge storage region D, and the electrons(electric charges) stay in the charge storage region C1 and the chargestorage region D. Thus, when reading data from the memory cell, fringecurrents are likely to occur. Consequently, when reading data from thememory cell, by applying a voltage having an opposite sign to a voltageapplied to the selected word line WL2 to the non-selected word lines WL1and WL3, the effective channel width W1 in the threshold voltage of thetransistor configuring the selected memory cell can be made narrow.Furthermore, advantageous effects of the present invention thatsuppresses the generation of fringe currents become large.

With reference to exemplary embodiments thereof, a semiconductor deviceis disclosed. The semiconductor device includes a plurality of memorycells that are provided in a matrix and that have a charge storage layermade of an insulating film that is provided on a semiconductor substrateand a plurality of word lines that are provided on the charge storagelayer. A plurality of memory cells that are arranged in a single lineamong the plurality of memory cells arranged in the matrix are coupledto the same word line. The semiconductor device further includes anapplication section that when reading data from a selected memory cellselected from the plurality of memory cells, applies a voltage to aselected word line to be coupled to the selected memory cell among theplurality of word lines. The application section applies a voltage thathas a polarity that is opposite to the voltage applied to the selectedword line to non-selected word lines arranged on both adjacent sides ofthe selected word line.

In one embodiment, the application section may keep applying a voltageto the non-selected word lines while applying a voltage to the selectedword line. According to such arrangement, when reading data from thememory cell, generation of fringe currents can be suppressed, and areading margin can be made large.

In one embodiment, the selected word line and the non-selected wordlines can be provided on the same charge storage layer. According tosuch arrangement, electric charges are also stored in the charge storagelayer in the vicinity of the selected word line, whereby fringe currentsare likely to occur. Thus, advantageous effects of the present inventionof suppressing generation of fringe currents become large.

In one embodiment, the charge storage layer can be made of a siliconnitride film. Also, in the above-described arrangement, electrons may bestored in the charge storage layer by hot electron effects. According tosuch arrangement, electric charges are stored in the charge storagelayer in the vicinity of the selected word line, whereby fringe currentsare likely to occur. Thus, advantageous effects of the present inventionof suppressing generation of fringe currents become large.

In one embodiment the arrangement may further include: a plurality ofbit lines provided crossing the plurality of word lines in thesemiconductor substrate so that a plurality of memory cells arranged ina single column among the plurality of memory cells arranged in a matrixare coupled to the same bit lines.

According to the present invention, when reading data from the memorycell, generation of fringe currents can be suppressed, and degradationof the effective threshold voltage can be suppressed. Consequently, areading margin can be made large.

In one embodiment, during the applying of the voltage to the selectedword line, the applying of the voltage having the opposite polarity tothe voltage applied to the selected word line to the non-selected wordlines can be performed.

The foregoing descriptions of specific embodiments have been presentedfor purposes of illustration and description. They are not intended tobe exhaustive or to limit the invention to the precise forms disclosed,and obviously many modifications and variations are possible in light ofthe above teaching. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, to thereby enable others skilled in the art to best utilizethe invention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

The invention claimed is:
 1. A semiconductor device comprising: aplurality of memory cells provided in a matrix and having a chargestorage layer; a plurality of word lines provided on the charge storagelayer; and an application section that when reading data from a selectedmemory cell selected from the plurality of memory cells, applies avoltage having an opposite polarity to the voltage applied to a selectedword line to non-selected word lines positioned adjacent each side ofthe selected word line.
 2. The semiconductor device according to claim1, wherein the application section keeps applying a voltage to thenon-selected word lines while applying a voltage to the selected wordline.
 3. The semiconductor device according to claim 1, wherein theselected word line and the non-selected word lines are provided on thesame charge storage layer.
 4. The semiconductor device according toclaim 1, wherein the charge storage layer is made of a silicon nitridefilm.
 5. The semiconductor device according to claim 1, whereinelectrons are stored in the charge storage layer by hot electroneffects.
 6. The semiconductor device according to claim 1, furthercomprising: a plurality of bit lines that cross the plurality of wordlines in the semiconductor substrate so that a plurality of memory cellsarranged in a single column among the plurality of memory cells arrangedin a matrix are coupled to the same bit lines.
 7. The semiconductordevice according to claim 1, wherein electric charges are stored in thecharge storage layer in the vicinity of the selected word line.
 8. Aflash memory device, comprising: input components; output components;and data storage components comprising: a plurality of memory cellsprovided in a matrix and having a charge storage layer; a plurality ofword lines provided on the charge storage layer; and an applicationsection that when reading data from a selected memory cell, applies avoltage having an opposite polarity to the voltage applied to a selectedword line to non-selected word lines positioned adjacent each side ofthe selected word line.
 9. The flash memory device according to claim 8,wherein the application section keeps applying a voltage to thenon-selected word lines while applying a voltage to the selected wordline.
 10. The flash memory device according to claim 8, wherein theselected word line and the non-selected word lines are provided on thesame charge storage layer.
 11. The flash memory device according toclaim 8, wherein the charge storage layer is made of a silicon nitridefilm.
 12. The flash memory device according to claim 8, whereinelectrons are stored in the charge storage layer by hot electroneffects.
 13. The flash memory device according to claim 8, furthercomprising: a plurality of bit lines that cross the plurality of wordlines in the semiconductor substrate so that a plurality of memory cellsarranged in a single column among the plurality of memory cells arrangedin a matrix are coupled to the same bit lines.
 14. The flash memorydevice according to claim 8, wherein electric charges are stored in thecharge storage layer in the vicinity of the selected word line.
 15. Amethod for controlling a semiconductor device comprising a plurality ofmemory cells arranged in a matrix, the method comprising: applying, whenreading data from a selected memory cell selected from the plurality ofmemory cells, a voltage to a selected word line that is coupled to theselected memory cell; and applying a voltage having an opposite polarityto the voltage applied to the selected word line to the non-selectedword lines positioned adjacent each side of the selected word line. 16.The method for controlling a semiconductor device according to claim 15,wherein, during the applying of the voltage to the selected word line,the applying of the voltage having the opposite polarity to the voltageapplied to the selected word line to the non-selected word lines isperformed.
 17. The method for controlling a semiconductor deviceaccording to claim 15, wherein a voltage is applied to the non-selectedword lines while applying a voltage to the selected word line.
 18. Themethod for controlling a semiconductor device according to claim 15,wherein the selected word line and the non-selected word lines areprovided on the same charge storage layer.
 19. The method forcontrolling a semiconductor device according to claim 15, wherein thecharge storage layer is made of a silicon nitride film.
 20. The methodfor controlling a semiconductor device according to claim 15, whereinelectrons are stored in the charge storage layer by hot electroneffects.